Joey Carbery has suffered a fractured wrist and could be sidelined for up to two months.
The Irish Rugby Football Union (IRFU) has confirmed playmaker Carbery's injury – sustained during Saturday's 23-20 win over Fiji – as a wrist fracture, not an arm problem as first thought.
The 22-year-old will miss Saturday's autumn Test against Argentina in Dublin, opening the door for Munster's Ian Keatley to understudy for frontline fly-half Johnny Sexton.
— Irish Rugby (@IrishRugby) November 20, 2017
"Joey Carbery suffered a fractured wrist and has been ruled out of the remaining fixture of the series," the IRFU confirmed in a statement.
Carbery impressed with ball in hand in Saturday's edgy win over Fiji, where Ireland made 13 changes from their record 38-3 victory over South Africa.
Head coach Joe Schmidt will bring back his raft of frontline stars to face Argentina this weekend, but Carbery's absence will prove a blow.
— Munster Rugby (@Munsterrugby) November 20, 2017
Ireland want Carbery to blossom into a fly-half to challenge Sexton's seniority, but Leinster have deployed the attacking talent predominantly at full-back this term.
Flanker CJ Stander climbed off the bench to steer Ireland to their slender Fiji victory, taking the captain's armband from Rhys Ruddock when joining the fray.
The 27-year-old admitted his honour at his captaincy cameo, then called on Ireland to refocus quickly to face the powerful Pumas this weekend.
"It's a learning experience for everyone; you learn a lot if it's not a big margin," said Stander, of the tight victory over Fiji.
"I think you learn a lot from each other and as players. As we look back, the main turnovers were in the first half.
— Munster Rugby (@Munsterrugby) November 20, 2017
"We just need to look after the ball and make sure we get through a few more phases and control the game the way we want to play it. Just look after the breakdown. A few times they got in there and slowed down our attack to put us on the back foot.
"I was excited (to be captain). When you get a call to go on it's a massive honour, I just said to the referee: 'I'm CJ Stander and I'm the captain now'.
"And I said about the breakdown what I felt was going wrong. He said 'perfect' and we went on.
"You just make yourself known so he knows who you are and if he looks for you he knows where to find you.
"Argentina are a physical side. Their forwards especially run hard. They play well, there's a lot of continuity in the team, they know each other very well and they're not afraid to attack from anywhere and even go up in an aerial battle."